Glomerular filtration has previously been studied only by indirect means. Data obtained indicates that the glomerular capillary is uniquely permeable to water and small molecules and quite impermeable to larger molecules. The maintenance of normal glomerular permeability and permselectivity are essential both to normal excretion of water, solutes and metabolic wastes and to conservation of plasma proteins. Glomerular filtration has been demonstrated in isolated glomeruli. Videorecording of glomerular volume changes during filtration has permitted estimation of the ultrafiltration coefficient, Kf. The proposed studies will first refine the technique and establish optimal conditions for measuring filtration. Later studies will investigate the permeability of isolated glomeruli from several species, various developmental stages, and superficial and deep cortical regions. Effects of environmental, cellular and metabolic and hormonal factors on filtration will be noted. Hypotheses regarding the contributions of each factor to intrinsic glomerular filtration characteristics will be generated. These hypotheses may later be applied to pathologic states and lead to an understanding of glomerular dysfunction and suggestions for possible treatment of clinical renal disease.